This invention relates to a new catalytic chemical process for making cyclic alkylene carbonates.
Cyclic carbonates such as ethylene carbonate and propylene carbonate are useful solvents and chemical intermediates. Commonly used processes for making these cyclic esters include the reaction of phosgene with the appropriate glycol and the reaction of a chlorohydrin with carbon dioxide, both carried out in the presence of a base and thus involving the production of a large amount of salt as an undesirable waste by-product.
It is known that .beta.-brominated alkyl carbonates such as 2,3-dibromopropyl ethyl carbonate and 2-bromoethyl ethyl carbonate undergo pyrolysis on long heating at about 200.degree. C. to produce bromomethylethylene carbonate and ethylene carbonate, respectively, with ethyl bromide as a co-product in each case, see Pews, J.C.S. Chem. Comm., 1974, p. 119. It is also known that these brominated alkyl carbonates and their chlorinated analogs were converted to corresponding alkylene epoxides when they are heated in the presence of a quaternary ammonium or phosphonium salt. This reaction is described in applications of one of us and another, see Renga and Emmons, Ser. No. 095,002, filed Nov. 16, 1979, now U.S. Pat. No. 4,261,906, also Ser. No. 238,188, filed Feb. 25, 1981, entitled "Process for Making Vicinal Epoxides and Dihalides", same inventors.